1. Field of the Invention
The invention relates to an electrohydraulic control system for the actuation of an actuator in a motor vehicle. Systems of the generic type have an electrohydraulic control unit and convert electrical energy into mechanical work, or vice versa.
2. Description of the Related Art
Vehicle brake systems of the generic type have a high pressure pump and have nonreturn valves (inlet and outlet valves) for ventilating their expulsion space. An electromagnetically activatable inlet valve and an electromagnetically activatable outlet valve are provided for each wheel brake. In order to bring about a switching process in the intake and pressure paths of the high pressure pump between the anti-lock braking mode (feedback function) and autonomous pressure buildup (driving stability function), two additional electromagnetically activatable valves are provided per brake circuit (isolating valve TV and solenoid switching valve EUV). An isolating valve is used to disconnect a direct hydraulic connection between a pressure chamber of a pressure transducer (master brake cylinder) and an actuator (wheel brake). A switching valve makes it possible to feed pressure medium, with extraneous actuation, that is to say independently of human actuation, from a pressure chamber of the pressure transducer (or a tank, vessel or reservoir) in the direction of one or more actuators. Depending on the organization of the brake circuits in a brake system (for example diagonal or black/white division) and depending on the variant of the vehicle drive train (all wheel drive, front wheel drive or rear wheel drive) a total of 12 to 14 solenoid valves with corresponding boring in a receiving body have to be provided. This increases the costs for the boring and for the electromagnetically activatable valves. With the exception of rotational speed control which is partially performed by the electric motor, the consumption of energy or the loading on the vehicle's onboard electrical system is not taken into consideration. This procedure cannot be maintained for comfort-related additional functionalities such as, for example, an inter-vehicle distance controller, because it would lead to the scarce resources on offer being exhausted, and furthermore the assemblies would be unnecessarily heavily loaded in many load situations, with the result that the necessary interplay of loading cannot be complied with.
In quite general terms, in hydraulic systems a distinction is made between pressure control, volume flow control and power control. For the specific control of a delivered volume or of a supplied pressure in a high pressure pump it is possible to identify four basic methods of operation (cf. for example J. Ivantsyn; Hydrostatische Pumpen und Motoren [hydrostatic pumps and motors], 1st edition, 1993, Vogel Fachbuch Verlag).
In a first known control principle, the delivery capacity of an electromotively driven high pressure pump is controlled by controlling the rotational speed of the electric motor. In these systems, the electric motor has a mechanical operative connection to a hydraulic pump. The delivered volume flow depends on the rotational speed of the electric drive motor. The hydraulic pump does not have its own control systems with which the delivery flow, or the pressure, can be influenced. Stringent requirements are made of the electric motor. This is because it must be able to process both large volume flows with small load-side system pressures and small volume flows at high system pressures. The delivered volume flow is proportionate to the rotational speed of the electric motor, while the load-side system pressure is proportional to the torque applied by the electric motor. As a result, the electric motor of this electrohydraulic system is to be configured both in the direction of a high rotational speed and in the direction of a high torque. This increases the costs of the electric motors.
For this reason electrohydraulic systems in which the electric motor is operated at a constant rotational speed and in which a bypass is provided with a bypass valve have already been proposed. The delivered volume flow of the high pressure pump is controlled by adjusting the bypass valve. This principle requires the high pressure pump to continuously generate a desired volume flow which is then itself made available if no hydraulic work is to be carried out. As a result, the power loss increases, which is to be avoided in view of a strained situation of the vehicle's onboard electrical system and rising energy costs in a motor vehicle.
As a third solution, systems have been proposed in which the high pressure pump is mechanically coupled to a drive motor of a motor vehicle. The drive rotational speed of the high pressure pump is as a result dependent on the drive rotational speed of the motor vehicle. For this reason, corresponding measures have to be taken such that the high pressure pump itself can always make available the requested hydraulic power at low drive rotational speeds. The situation with comparably high drive rotational motor speeds is correspondingly reversed. In order to compensate for these disadvantages, a comprehensive mechanical adjustment capability of the high pressure pump has to be made available such as is the case, for example, by means of swash plates in air-conditioning compressors.
Finally, systems are known in which the delivery flow is controlled by an adjustable throttle on the intake volume flow, for example by means of an adjustable orifice. In this context, disadvantageous hydraulic effects such as, in particular, a noise nuisance or cavitation may occur.
An object of the present invention is to avoid the described disadvantages and to make available a simplified electrohydraulic control system which has an adjustable high pressure pump and which has an economic, compact design, consumption levels which spare resources and is also universally suitable for application outside a vehicle brake control system.